In the field of processing paper pulp, either by means of reclaiming pulp from a previously used paper product or from recovering pulp from digested wood chips, the process machinery and motor drive systems have changed little since the turn of this century. That is to say, paper pulp screening and refining apparatus, for example, primarily consists of a traditionally frame mounted rotating component, supported on its own mechanical support bearings, and provided with an external shaft to which the rotating component is driven. Generally, such pulp processing machinery, including but not limited to refiners, pulp pressure screens and the like, requires large amounts of power to be applied to such rotating components, either through direct shaft coupled or belted electric drive motors. Such arrangements, as commonly known, are inherently inefficient, expensive and potentially dangerous for at least the following reasons:
1. Four or more sets of support bearings and related bearing support structures are required, usually at least two for the rotating components and two for the motor armature.
2. Many pulp processing machines require that the paper pulp or other material to be processed be brought into a relatively central position and then moved in a relatively radial outward direction during processing. Such machines would benefit greatly from being able to bring in the material to be processed on an axial basis for uniform distribution, but that is not practical in most existing equipment designs due to the fact that the rotor shaft is solid and is positioned on the axis, and therefore requires that the material be brought in at an off-axis basis. This requires a needlessly greater complexity.
3. Since the process material in many instances cannot be brought in on the axis of rotation, it becomes necessary to provide openings in the rotating components so that material may be fed in a balanced condition to two or more working portions of the rotating structure. For example, in a refiner, the material must flow to the remote face of the center refining disk through radially offset openings in the disk provided for this purpose.
4. The separate drive motor requires external or open couplings shafts, pulleys, belts and like components, all of which require shielding to protect against possible injury, and requires seals to isolate the material being processed from the external rotating components.
The structural support arrangement for the rotating components of paper process machinery does not permit or enable ease of adjustment of the relative position of rotating components. For example, rotating components may be cone-shaped, such as in paper refiners, and refiner clearances are adjusted only by laboriously making corrections in the axial position of a non rotating component. The same is true for disk refiners where a radial rotor for refining paper stock is positioned between plates of an opposed pair of stator members. In such cases, the practice has been to provide auxiliary systems for moving the stator elements, as desired, while leaving the rotor suspended in a fixed or uncontrolled plane on its rotating support mechanism.
A further impediment to the creation of integrated paper pulp processing machine is the fact that drive motors have been traditionally designed for generic purposes, by motor manufacturers generally unfamiliar with the peculiar or particular requirements of the paper pulp processing industry, and likewise, paper pulp processing machinery has been designed with the underlying intent or understanding that such machinery will be driven by separately designed electric motor drives. Such conditions have provided little opportunity for integration of the common functions inherent in motor drive and in pulp processing rotary machinery.
This invention is an improvement to current rotating pulp processing machinery. It is designed to be used in the pulp and paper industries where equipment now incorporates a combination of oil or grease lubricated rotating assemblies and an external drive motor. This invention integrates a variable speed motor into the structure of the pulp or paper preparation equipment. The integration makes use of magnetic bearing systems for supporting the rotating component, both of the motor and of the pulp treating equipment and integrates, in some instances, the functions of pulp treating and driving torque or power.
In a preferred system, a rotor is supported on magnetic bearings, and the rotor as well as the bearings may be immersed or submerged partially or fully within the liquid being processed. The bearings levitate the rotor of the motor and control the rotor""s orbit and position. The rotor itself becomes, or directly drives, the rotating pulp processing component. Both rotor and bearing may be cooled by the process liquid.
More particularly, use is made of magnetic bearings and an integrated variable speed motor, such as a switched reluctance motor. The control of the magnetic bearings and the motor may themselves be integrated into a common control system for the complete unit.
By integrating the motor rotor with the process rotor, and utilizing the available magnetic bearing control systems, the position of the rotor may be controlled by the magnetic bearing systems to improve the performance of the process apparatus and by providing fine tuning of the rotor position in equipment which heretofore has not had this capability. A further advantage of the system is that the motor rotor now becomes an integral part of the system within the pulp slurry and allows for the elimination of an external rotating assembly. Therefore a totally enclosed system is possible.
Switched reluctant motor technology is preferred. The rotors are not complicated and are light in weight. The electric current switching circuits are reliable. The rotors do not use windings or permanent magnets. Speed and rotation can be quickly controlled by the motor controller, thereby improving efficiency and providing high starting torque. Therefore, a pulp treating system has the advantages of an accurate variable speed control that permits process operation optimization with energy savings, pulp quality optimization, and substantial savings in installation costs, weight, floor space, and safety risks.
A further significant advantage resides in the fact that by combining the control of the process machinery with the control of the motor, the quality of product may be more fully controlled by a computer program.
Another object and advantage of the invention is that the rotating and non-rotating parts do not contact each other during use so part wear and power loss are minimized. Utilization or duty cycle time is maximized.
The quality of the product, such as paper pulp, can be tuned, while the critical dimensions in the relation between the rotor and the stator elements may be maintained throughout the life of the unit so that performance, if desired, can remain constant. Algorithms can be developed to improve unit performance where a particular programmed rotor orbit may be found to be beneficial over that of operating in a single plane of rotation as now required on conventional bearings.
A further important advantage of the integrated concept of this invention is the fact that the rotor itself may be made hollow to form an axial conduit for the flow of a pulp suspension. While a rotor may be integrated with, or may be driving a separate pulp treating component, (such as a refiner disk or a rotating screening element) a hollow rotor can substantially simplify the application of a pulp slurry to the working portion of the rotor, with reduced back pressure and lower pressure drop. Further, the entire unit may be integrated in such a manner that it can be quickly and easily placed into an in-line relationship with respect to existing conduits.
The use of a switch reluctance motor provides an ability to reduce noise. Further, such motor designs have the ability to alter rotational speeds very quickly, and this can be used to minimize high-frequency noise as now generated in such equipment.
Further, switched reluctance motors have been found to be more reliable than complex induction motors, providing easier start up and greater starting torque. The high starting torque means that the rotors can be shut down and started up again without the necessity for flushing out the rotors. As noted above, the rotors and stator of switched reluctance motors are singularly simple in construction and less subject to failure and lend themselves to integrated systems in which the rotor and even the stator can be in contact with the process liquid.
The elimination of conventional shaft sealing with oil/grease rotating assemblies eliminates a problem of maintenance, since such conventional equipment can fail due to water and/or pulp contamination through the seals and into the bearings.
The integration of the assembly removes the need for guarding the present type assemblies for safety purposes, to prevent exposed belts and pulleys operating at high speed and high power and inherently reduces the need for maintenance of such components. Where direct flexible couplings had been used before, these couplings are eliminated and therefore do not have to be maintained or guarded.
The overall installation and product costs to a consumer is reduced by reduced floor space, less complexity and weight, and by the flexibility of a totally sealed unit.